Heart failure is the physiological state in which cardiac output is insufficient to meet the needs of the body and the lungs. Patients suffering from any of a number of forms of heart failure are prone to increased fluid in the body. Congestive heart failure (CHF) occurs when cardiac output is relatively low and the body becomes congested with fluid. There are many possible underlying causes of CHF, including myocardial infarction, coronary artery disease, valvular disease, and myocarditis. Chronic heart failure is associated with neurohormonal activation and alterations in autonomic control. Although these compensatory neurohormonal mechanisms provide valuable support for the heart under normal physiological circumstances, they also have a fundamental role in the development and subsequent progression of CHF. For example, one of the body's main compensatory mechanisms for reduced blood flow in CHF is to increase the amount of salt and water retained by the kidneys. Retaining salt and water, instead of excreting it into the urine, increases the volume of blood in the bloodstream and helps to maintain blood pressure. However, the larger volume of blood also stretches the heart muscle, enlarging the heart chambers, particularly the ventricles. At a certain amount of stretching, the heart's contractions become weakened, and the heart failure worsens. Another compensatory mechanism is vasoconstriction of the arterial system. This mechanism, like salt and water retention, raises the blood pressure to help maintain adequate perfusion.
Glomerular filtration rate (GFR), the rate at which the kidney filters blood, is commonly used to quantify kidney function and, consequently, the extent of kidney disease in a patient. Individuals with normal kidney function exhibit a GFR of at least 90 mL/min with no evidence of kidney damage. The progression of kidney disease is indicated by declining GFR, wherein a GFR below 15 mL/min generally indicates that the patient has end stage renal disease (ESRD), which is the complete failure of the kidney to remove wastes or concentrate urine.
Cardiovascular problems, such as but not limited to, inadequate blood flow or chronic hypertension, may lead to fluid retention in the kidneys, chronic kidney disease, lowered GFR, renal failure or even ESRD. For example, hypertension is considered the second most prevalent cause for kidney failure (after diabetes). It is been estimated that hypertension causes nephrotic damage and lowers GFR.
Therefore, it would be desirable to provide apparatus and methods to improve blood flow to prevent disease, improve body functionality, and/or treat conditions that would benefit from modified body fluid flow. For example, it would be desirable to treat heart failure, treat hypertension, prevent kidney disease, improve kidney functionality, and/or prevent blood clots from flowing through vasculature to sensitive portions of the body, such as the brain, in order to prevent strokes.